1. Field of the Invention
This invention relates to a semiconductor layer containing, as a principal constituent, a Groups III-V semiconductor compound, which may be represented by the general formula AlxGayInzN, wherein x represents a number satisfying the condition 0≦x<1, y represents a number satisfying the condition 0<y<1, and z represents a number satisfying the condition 0<z<1, with the proviso that x+y+z=1. This invention also relates to a process for forming the semiconductor layer. This invention further relates to a semiconductor light emitting device, which comprises the semiconductor layer, and a semiconductor light emitting apparatus, which comprises the semiconductor light emitting device.
2. Description of the Related Art
In the field of light emitting diodes, GaN type materials have been developed, and high-efficiency blue to green light emitting diodes have been used in practice. The light emitting diodes for the three primary colors of red, green, and blue have thus become available, and application of the light emitting diodes to displaying use applications, and the like, has come into existence.
Also, recently, a white light emitting diode has been used in practice. The white light emitting diode comprises a blue light emitting diode and fluorescent substances located around the blue light emitting diode, which fluorescent substances are capable of being excited by the light having been produced by the blue light emitting diode and are thus capable of producing light having wavelengths falling within wavelength regions different from the blue wavelength region. With the white light emitting diode, the light having been produced by the blue light emitting diode and the light having been produced by the fluorescent substances are combined together, and white light is thereby obtained.
In the field of semiconductor lasers, semiconductor lasers capable of producing laser beams having wavelengths falling within the range of 375 nm (of the near ultraviolet light wavelength region) to 450 nm (of the blue light wavelength region) have been used in practice. However, under existing circumstances, there is no prospect of use of semiconductor lasers, which are capable of producing laser beams having longer wavelengths falling within the green to yellow light wavelength region, in practice.
An AlGaInN type semiconductor laser utilizing a ZnO base plate as a base plate has been proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-017484. One of causes for the limitation of the possible wavelengths of the laser beams, which are produced by the currently used semiconductor lasers, to the blue light wavelength region of 450 nm is the use of the GaN base plate as the base plate. It is considered that, in cases where a ZnO base plate having a lattice constant larger than the lattice constant of the GaN base plate is used, the band gap energy of the AlGaInN type material, which is lattice matched with the ZnO base plate, is capable of being set to be small, and that a semiconductor laser producing a laser beam having a longer wavelength is thus capable of being obtained.
However, with the AlGaInN type semiconductor laser utilizing the ZnO base plate as the base plate as proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-017484, the problems with regard to production are encountered. Specifically, in cases where the AlGaInN material is caused to grow on the ZnO base plate by use of a metalorganic vapor phase epitaxy technique (hereinbelow referred to as the MOVPE technique), which has widely been used for the production of the semiconductor lasers, the oxygen atom of ZnO of the base plate is eliminated, the base plate itself deteriorates before the crystal grows, and a crystal having good quality is not capable of being caused to grow. Also, with the semiconductor laser as proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-017484, the semiconductor active layer has a bulk structure. The semiconductor laser as proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-017484 thus has a device structure such that high efficiency characteristics are not always capable of being obtained.
As described above, the semiconductor laser as proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-017484 has the production problems with regard to the deterioration of the base plate and the low crystalline characteristics of the AlGaInN material and the problems with regard to the device structure in which the semiconductor active layer has the bulk structure. Therefore, with the semiconductor laser as proposed in, for example, Japanese Unexamined Patent Publication No. 1(1989)-017484, it is not always possible to obtain a semiconductor laser having a high efficiency and good light emission characteristics. Also, in the examples described in, for example, Japanese Unexamined Patent Publication No. 1(1989)-017484, only the production of blue to violet laser beams is described. Thus in, for example, Japanese Unexamined Patent Publication No. 1(1989)-017484, nothing is reported with respect to the production of a laser beam having a long wavelength falling within the green light wavelength region or a longer wavelength region.
Further, with the conventional light emitting diodes, the light emitting diodes alone are not capable directly producing the white light. Specifically, heretofore, the fluorescent substances are excited by the blue light emitting diode, the light having been produced by the blue light emitting diode and the light having been produced by the fluorescent substances are combined together, and the white light is thus indirectly obtained. In cases where the light emission efficiency is taken into consideration, it is desired that a white light emitting diode capable of directly producing the white light is capable of being obtained.